Field experiments were carried out in 2001 and 2002 to examine the lodging-resistance characteristics of various rice cultivars bred for the Tohoku region of Japan including the widely-cultivated cultivars (WCC) and the newly-released cultivars (NRC). The difference in these characteristics between the plants grown under standard (CONT) and nitrogen-free basal dressing accompanied with sparse planting density (BNo) practices was also analyzed. The lengths of the lower internodes and culms were often shorter in NRC than in WCC. Bending moment by whole plant was not different between NRC and WCC, but the breaking strength at the basal internode (IV) with leaf sheaths was often larger in NRC than in WCC. As a result, the lodging index was smaller in the former than in the latter. Breaking strength at the basal internode (IV) without leaf sheaths was also often larger in NRC than in WCC due to a larger cross section modulus or bending stress in NRC. Although the lengths of the upper internodes (I+II+III) were not different between BNo and CONT, the lower internodes (IV+V) were shorter in BNo, resulting in the shortened culms in BNo, especially in the long-culm cultivars. Breaking strength at the basal internode (IV) with leaf sheaths was significantly larger in BNo than in CONT, and thus the lodging index was smaller in BNo. The breaking strength at the basal internode (IV) without leaf sheaths and its two components, cross section modulus and bending stress, were also significantly larger in BNo than in CONT, particularly in the long-culm cultivars. These results suggest that besides creating new cultivars with short and stiff lower internodes, cultivation with sparse planting density accompanied with application of a small amount of nitrogen fertilizer in the early growth stage like BNo may also effectively increase the lodging resistance in rice plants.

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To study whether wild rice species have genes that may increase potential photosynthetic capacities of rice cultivars, we generated BC₂ populations by reciprocally backcrossing Oryza rufipogon (W630) with O. sativa cv. Nipponbare and IR36; N-BC₂ populations and IR-BC₂ populations, respectively. We measured the oxygen evolution rates (OER) of single leaves under saturating light and CO2 as the maximum photosynthetic rates and the contents of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase. Several lines in each BC₂ population had significantly higher OERs than parental cultivars, and 14–25% of plants in BC₂ populations had higher OERs than the highest values in parental cultivars. The highest OERs in BC₂ populations were about 60% higher than average OERs in parental cultivars. The BC₂ populations contained 30–40% more Rubisco than parental cultivars. The Rubisco activase contents in N-BC₂ populations were 15–30% lower than that in Nipponbare. Cytoplasms derived from O. rufipogon and O. sativa had different effects on the contents of Rubisco and Rubisco activase particularly in N-BC₂ populations. In several lines of each BC₂ population the OERs had positive correlations with the contents of Rubisco and/or Rubisco activase. These results suggest that O. rufipogon can be used as a source of germplasm to enhance the photosynthetic capacity of O. sativa.

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Dwarf lilyturf (Ophiopogon japonicus K.), used as a weed-suppressing cover crop and a medicinal plant, was suggested to be a promising natural herbicide to control weeds in the rice field through its allelopathic potential. Allelopathic chemicals from the dwarf lilyturf were identified and their growth-inhibiting effects on two major weeds in the rice field in Japan were examined. High pressure liquid chromatograph (HPLC) analysis showed the existence of at least six allelopathic chemicals, viz., salicylic acid, syringic acid, syringaldehyde, vanillic acid, ρ-hydroxybenzoic acid and sinapic acid in dwarf lilyturf plant. The chemical detected at the highest concentration was salicylic acid (251.04 μg g^-1), which occupied more than half of total allelopathic chemicals detected (317.16 μg g^-1), followed by syringic acid (37.30 μg g^-1), syringaldehyde(13.30 μg g^-1) and sinapic acid (11.03 μg g^-1). The chemicals detected at the lowest concentration was vanillic acid (1.69 μg g^-1). Salicylic acid displayed the most inhibitory effects on germination and growth of both barnyardgrass (Echinochloa crusgalli L.) and monchoria (Monochoria vaginalis P.). This compound might play a key role in dwarf lilyturf allelopathy.

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Five cotton (Gossypium hirsutum L.) cultivars were grown in the field in Xinjiang, China to evaluate their adaptability to arid conditions in terms of leaf temperature, transpiration rate and leaf movement. Leaf temperature was higher in the morning and lower in the afternoon as compared with air temperature. There were large differences in the transpiration rate represented by the flow rates of stem sap per unit leaf area (FRSS) among the cotton cultivars. The transpiration rate in cotton generally depended on vapor pressure deficit (VPD). In the cultivars with a low transpiring ability, however, the influence of VPD was lower in the higher range of VPD. Cultivars with higher transpiring ability tended to have higher intercepted radiation per unit leaf area (IRL), i.e., to show active diaheliotropic leaf movement. The higher transpiring ability of cotton might be able to reduce heat stresses caused by diaheliotropic leaf movement and be profitable for yield under the arid conditions.

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Grain yield under wet season (WS) conditions has gradually received more attention due to looming scarcity of irrigation water, which limits the area for planting to flooded lowland rice in the dry season in the tropics. This study was conducted to determine (1) grain yield of IRRI (International Rice Research Institute)-released rice cultivars under WS conditions and (2) if panicle size (spikelet number per panicle) is an important trait that influences grain yield in the WS. Field experiments were conducted at the IRRI farm in the 2000 WS and 2001 WS using 14 IRRI-released conventional and two F₁ hybrid cultivars under irrigated lowland conditions. Grain yield and yield-related traits were measured at maturity. Grain yield of tested cultivars ranged from 4.5 to 7.0 t ha^-1 in the 2000 WS and from 4.1 to 5.6 t ha^-1 in the 2001 WS. Large differences in panicle number and panicle size were observed among cultivars. All cultivars had small to intermediate panicle size ranging from 63 to 114 spikelets per panicle. Among all the measured yield-related traits, panicle size had the most consistent and closest positive correlation with grain yield. These results suggest that it is possible to improve maximum attainable yield in WS by breeding cultivars with larger panicle size. However, whether other cultivar groups such as the tropical japonica with large panicles (150-200 spikelets per panicle) would confer high yield in WS remains to be studied.

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The structural changes of crystalloplastids during calcium oxalate crystal idioblasts growth in Japanese yam tubers were examined by transmission electron microscopy. Idioblasts developed in the cortex of tubers during the tubers development were large and elliptic and contained many crystalloplastids. The crystalloplastids were shown to have novel morphological characterizations. The single or multiple obvious electron-translucent parts without membrane structures were formed in the crystalloplastids during the crystal formation. Coincidentally, the electron-dense parts containing plastid ribosomes and tubular membranes were formed at the periphery of crystalloplastids. During further progress of crystal formation, obvious electron-translucent parts enlarged and finally electron-dense parts disappeared, forming the crystalloplastids similar to small vacuoles and/or vesicles. The majority of such crystalloplastids entered and was incorporated into the central vacuoles of idioblasts during crystal formation. The plastids remaining in the cytoplasm of mature idioblasts were proplastid-like organelle. Thus, the fate of crystalloplastids with growth of idioblasts was shown in Japanese yam tubers. It was suggested that the incorporation of crystalloplastids into central vacuoles of the idioblasts was one of the processes of material transportation involved in calcium oxalate crystal formation.

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We investigated the kinds of active oxygen species leading to the destruction of chloroplast ultrastructure in salt-stressed rice plants. After the seedlings were grown for 3 wks, leaf segments (5 mm square) were cut from the middle portion of the 5th leaves. Leaf segments were incubated in 200 mM NaCl under dark or light conditions for 24 hr. The chlorophyll content in the leaf segments drastically decreased in light between 12- and 24 hr in 200 mM NaCl, but, no reduction was observed in the dark. In electron microscopic studies, 200 mM NaCl caused swelling of thylakoids and destruction of thylakoid membranes in light. On the other hand, no ultrastructural changes were observed under dark condition. In one experiment, leaf segments were incubated in 200 mM NaCl for 24 hr in light after preincubation with antioxidants for 12 hr in light. Pretreatment with ascorbate and benzoate, which scavenge H₂O₂ and ·OH, respectively, effectively suppressed the reduction of chlorophyll content and the destruction of chloroplasts by NaCl in light. However, Tiron and DABCO, which scavenge O₂^- and ¹O₂, respectively, could not suppress the effects of salt stress in light. Fe-SOD activity was increased about eight time by salt stress (200 mM NaCl), but, catalase activity was reduced to 69% of the control and ascorbate peroxidase activity was not affected by NaCl. These results suggested that salt-induced injury in chloroplasts is dependent on light, and that H₂O₂ and ·OH are responsible for the deleterious effects of salt stress on chlorophyll content and chloroplast ultrastructure.

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Analysis of phenotypic performance in the field in combination with molecular analysis provides useful information to increase the efficiency in plant breeding programs. We investigated: (i) the relationship between phenotypic performance and genetic diversity determined using simple sequence repeat (SSR) markers, (ii) the possibility of grouping inbred lines based on phenotypic performances and (iii) the genotypic and phenotypic variance of yield, yield components and primary agronomic traits among inbred lines. Among 22 sorghum inbred lines, grain yield per plot and days to flowering were less representative as phenotypic markers. However, the following six phenotypic traits showed high heritability; 1000-grain weight, ear length, plant height, stalk diameter, dry weight and harvest index, and were useful as phenotypic markers. The data obtained using SSR markers significantly correlated with those of phenotypic performance in this study, and the grouping of inbred lines based on the combination of the performance of six phenotypes was similar to that based on SSR markers. On the basis of phenotypic performance, four inbred lines, D12, H11, C9xH13 and C9xH11, were selected as promising parents for plant breeding programs.

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Appropriate plant height, tiller number and heading date are important traits for maximizing rice production. In order to understand the genetic basis of the relationships among these three plant traits, we mapped quantitative trait loci (QTLs) using a recombinant inbred population and detected two-locus interactions for plant height and tiller number at two growth stages and for heading date in two years. There were significant negative correlations between tiller number and plant height, and between tiller number at maturity and heading date. A significant positive correlation was observed between heading date and plant height at maturity. A total of 29 QTLs for the three traits were identified over the two years. Results show that QTLs and majority of two-locus interactions for plant height and tiller numbers at 35 days after transplanting were different from those at maturity, indicating that different genes and interactions control the traits at different developmental stages. A large proportion of QTLs and interactions could only be detected in one year, suggesting that QTLs and two-locus interactions for the traits were dependent on the environment. Results suggest that pleiotropy and/or close linkage of genomic regions and pleiotropy of common two-locus combinations may be the genetic basis for the close correlations among the three traits. A QTL with a large effect for heading date, which was located in RG424-RZ667 on chromosome 6, also showed large effects on tiller number and plant height at maturity.

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A total of 350 rapid amplified polymorphic DNA (RAPD) primers and 100 simple sequence repeat (SSR) primer pairs were screened to identify polymorphic markers associated with powdery mildew resistance. Only primer OPP15 produced a 900bp reproducible DNA fragment (OPP15₉₀₀) in the resistant parent cv. Brock and most of the resistant individuals, but this DNA fragment was absent in susceptible parent Jing411 and Line 015. The progeny, including 218 resistant and 81susceptible lines, derived from a cross Line 015/Brock//Jing411² was used for linkage analysis. 209 resistant and 8 susceptible individuals yielded OPP15₉₀₀ products, but 73 susceptible and 9 resistant ones yielded no OPP15₉₀₀ products. One dominant RAPD molecular marker OPP15₉₀₀ linked to powdery mildew resistance gene was identified in Brock with a genetic distance of 6.0 cM. A SSR marker Xgwm114 was also proved to link with the powdery mildew resistance and genetic distance of 9.3 cM. These two new molecular markers are useful for facilitating selection and pyramiding the resistance genes in wheat breeding.

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Growth enhancement by drainage during seedling establishment was compared with seed coating with calcium peroxide in rice direct-sown into puddled and leveled soil. Coated and noncoated seeds were sown about 10 mm deep, three times from April to June at two locations (Niigata and Ibaraki, Japan). Seed coating with calcium peroxide accelerated seedling emergence at an early stage, whereas drainage during 10 to 13 days after sowing promoted it at a late stage. Although drainage was less effective in increasing the number of finally emerged seedlings than seed coating with calcium peroxide, the drainage clearly improved seedling establishment. Seed coating with calcium peroxide enhanced shoot elongation during seedling emergence. In contrast, drainage somewhat inhibited shoot elongation at this time, but promoted it after drained soil was flooded. Drainage also increased the dry weight of shoots more than flooding after seedling emergence. These results indicate that seed coating with calcium peroxide enhances plant growth during seedling emergence, whereas drainage after sowing promotes plant growth mainly after seedling emergence. This suggests that seed coating with calcium peroxide accelerates seedling emergence, but drainage after sowing enhances seedling establishment.

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To elucidate the effect of no-tillage practice on the root system development and productivity in a wheat-soybean rotation system in Japan, we continuously cultivated these crops under tilled and non-tilled field conditions and compared the growth and yield for three years. Effect of presence or absence of tillage on the root growth was evaluated by the quantitative analysis for the root systems obtained by the core sampling method. The total shoot biomass and yield of wheat were significantly higher in the tilled field than in the non-tilled field in the first and second seasons, whereas, they were significantly higher in the non-tilled field in the third season. On the other hand, no significant difference between the tilled and non-tilled field was found in the soybean yield for the three seasons. Root length per unit area had a significant positive correlation with both the total shoot biomass and yield in wheat but not in soybean. The continuous no-tillage practice improved the soil condition for root development and resulted in an enhancement of the shoot growth and yield of wheat. In soybean, on the other hand, the root system development greatly fluctuated from season to season, especially, in the non-tilled field, but the productivity in the non-tilled field was relatively stable equivalent to that in the tilled field. Thus, stable production equivalent to that obtained by conventional tillage can be achieved by the no-tillage practice in a typical Japanese climate regardless of the fluctuation in root system development.

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The effects of nitrogen (N) application (32, 72 and 112 kg N ha^-1 in 2000, and 32, 92 and 152 kg N ha^-1 in 2001) and water-saving irrigation and their interaction on grain yield and yield components of the rice cultivar Champa-Kamphiroozi, which is a local cultivar in a semi-arid area in the south of Islamic Republic (I.R.) of Iran, were investigated. The plants were cultivated under sprinkler irrigation (1.0 ET_p and 1.5 ET_p), intermittent flooding (1-day and 2-day intervals) and continuous flooding (control). The experiments were conducted on a clay loam-clay soil under a semi-arid environment using four replications in a split plot design with irrigation method as main plots and N levels as subplots. The results indicated that intermittent flooding irrigation at 2-day intervals was as effective as continuous flooding for grain yield, showing high water-use efficiency (WUE). The soil moisture tension in the root zone before each irrigation under this condition was -300 to -400 cm. Sprinkler irrigation and intermittent flooding increased WUE by 20 to 60%, compared with continuous flooding, and the increase in N application rate to 112-152 kg ha^-1 increased grain yield under any irrigation condition. Under sprinkler irrigation, grain yield was low and percentage of unfilled grain was high, although WUE was high. However, by adopting sprinkler irrigation, the amount of nitrogen fertilizer application necessary for cultivation was reduced. Furthermore, when nitrogen application must be limited due to groundwater pollution, the amount of nitrogen fertilizer necessary for cultivation can be reduced.

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In Gunung Batin, the southern end of Sumatra Island, Indonesia, cassava is widely cultivated on gently sloping areas for starch materials. The monoculture system and/or the intercropping system without legume plants commonly adopted in this region may tend to accelerate soil degradation. The objective of this study is to compare the productivity among several cassava cropping patterns to propose the most beneficial one in this region. A field experiment of five cropping patterns {cassava (Manihot esculenta Crantz) single-cropping, three cassava-based intercropping patterns, and a crop rotation} was conducted for three years. The cropping pattern that recorded the highest net income varied with the year. In 1997, the driest year of the past several decades, cassava single-cropping was the highest in income. The proposed intercropping system {cassava/(maize—soybean—cowpea)} was the highest in 1998, a year with moderate rainfall. In 1999, when severe insect damage occurred to legume crops, the farmers' conventional intercropping was the highest. In an average of the three years, the proposed intercropping pattern was same as cassava single-cropping, although cowpea cultivation as the dry season cropping was not possible in this region. The amount of soil erosion was relatively high in cassava monoculture in comparison with the other intercropping and crop-rotation systems. Cassava roots penetrated to only 0.5 m deep and extended 1 to 2 m in a horizontal direction depending on the planting density. These results lead to the conclusion that the proposed cassava cropping system would be the most beneficial in terms of economy and control of soil erosion.

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At mid-elevation terraces in the southern part of Sumatra Island, Indonesia, cassava is widely cultivated as one of the most important cash crops for farmers. However, the prominent cassava cultivation system includes the intercropping of cereal crops and rapidly depletes soil fertility. Hence establishment of a sustainable food-crop production system without cassava cultivation is required. A three-way experiment with maize-soybean-cowpea sequential cropping was designed to investigate the following main effects: tillage or no-tillage, mulching or no-mulching and government recommendation or farmers' traditional fertilization. Crop productivity and soil erosion were used as indicators of sustainability. At the end of the experiment, root system development of soybean was assessed to elucidate the cumulative effects of treatments on the soil environment for root growth. Fertilization treatments increased yields in all years, whereas mulching significantly increased only from the third year. The no-tillage treatment tended to reduce yields. Soybean root growth at surface level was markedly reduced by no-tillage and slightly improved by mulching. Erosion was reduced by mulching, no-tillage, and fertilization by the government recommendation. Because of its cumulative effect on increasing soil fertility and reducing erosion, the practice of mulching was highly recommended. A sufficient amount of fertilization (government level) was also recommended to maintain the fertility and to support sufficient plant growth to minimize erosion. The no-tillage practice was not recommended because it reduced crop yields, although the treatment efficiently controlled soil erosion.

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